Soil Phosphorus Distribution Research Articles

Spatial and seasonal distributions of soil phosphorus in a short-term flooding wetland of the Yellow River Estuary, China

Soil cores were collected at a depth of 60cm along a sampling belt perpendicular to the Yellow River of the Yellow River Estuary and were collected in both summer and fall of 2007 and the spring of 2008 to investigate spatial and seasonal dynamics of soil phosphorus in a short-term flooding wetland. Our results showed that total phosphorus (TP) levels were lowest in spring, followed by those in summer and the maximum level was in fall along the sampling belt. Lower TP levels were observed at Site 3 in summer and fall, whereas the lowest TP levels appeared at Site 1 in spring. All available phosphorus (AP) levels were higher in fall than that in spring except for Site 4. However, in summer, AP contents showed a “decreasing before increasing” tendency along the sampling belt. TP contents in profile soils exhibited a decreasing tendency from summer to next spring, whereas AP levels increased slightly from summer to fall and decreased from fall to the next spring. TP contents increased and then decreased along soil profiles in summer and spring, whereas they showed a “decreasing before increasing” tendency in fall. The mean AP levels and AP: TP ratios generally decreased along soil profiles in three sampling seasons. TP stocks ranged from 419.40mgm−2 to 578.45mgm−2 and generally exhibited an increasing tendency from Site 1 to Site 5. Approximately 50% of TP stocks accumulated in the top 20cm soils. Higher TP stocks in the top 60cm soils were observed in summer and fall at each of five sampling sites than in spring (p<0.05). Correlation analysis showed that Soil TP levels were significantly correlated with soil bulk density (BD) and salinity, and AP contents were significantly correlated with soil depth and pH values. TP stocks were significantly impacted by TP, BD and pH values.

Distribuição horizontal e vertical de fósforo em sistemas de cultivos exclusivos de soja e de integração lavoura-pecuária-floresta

O objetivo deste trabalho foi avaliar a distribuição horizontal e vertical do fósforo no solo e a produtividade de soja em sistemas de cultivos exclusivos e de integração lavoura-pecuária-floresta (ILPF). Foram avaliados os tratamentos: floresta plantada de eucalipto; lavoura de soja e milho safrinha consorciado com Urochloa brizantha 'Marandu'; pastagem de U. brizantha; sistema de ILPF; e duas áreas controle, com floresta nativa e pousio. O solo foi coletado nas camadas de 0-5, 5-10, 10-20 e 20-30 cm, para determinação das características químicas. As avaliações foram realizadas no segundo ano agrícola após a implantação do experimento. No sistema de ILPF, solo e produtividade foram avaliados em quatro transectos equidistantes, no centro do renque e a 3, 6, 10 e 15 m do renque, nas faces norte e sul. Os teores de P disponível (Mehlich-1) foram maiores nas camadas superficiais do solo, nos sistemas com soja/milho safrinha e com ILPF. No ILPF, os teores de P disponível não diferiram entre as distâncias do renque das árvores, e a produtividade de soja não diferiu da observada no sistema com soja/milho safrinha. Portanto, com dois anos de implantação, o sistema ILPF ainda não é capaz de interferir marcadamente nas características químicas do solo e na produtividade da soja.

Spatial and seasonal distributions of soil phosphorus in a typical seasonal flooding wetland of the Yellow River Delta, China

Soil samples from 0 to 100 cm depth were collected in four sampling sites (Sites A, B, C and D) along a 250-m length of sampling zone from the Yellow River channel to a tidal creek in a seasonal flooding wetland of the Yellow River Delta of China in fall of 2007 and spring of 2008 to investigate spatial and seasonal distribution patterns of total phosphorous (TP) and available phosphorus (AP) and their influencing factors. Our results showed that TP contents in spring and AP contents in both seasons in surface soils increased with increasing distances away from the Yellow River channel. TP contents in surface soils (0–10 cm) followed the order Site A (698.6 mg/kg) > Site B (688.0 mg/kg) > Site C (638.8 mg/kg) > Site D (599.2 mg/kg) in fall, while Site C (699.6 mg/kg) > Site D (651.7 mg/kg) > Site B (593.6 mg/kg) > Site A (577.5 mg/kg) in spring. Generally, lower TP content (630.6 mg/kg) and higher AP level (6.2 mg/kg) in surface soils were observed in spring compared to fall (656.2 mg/kg for TP and 5.2 mg/kg for AP). Both TP and AP exhibited similar profile distribution patterns and decreased with depth along soil profiles with one or two accumulation peaks at the depth of 40–80 cm. Although the mean TP content in soil profiles was slightly higher in spring (635.7 mg/kg) than that in fall (628.0 mg/kg), the mean TP stock was obviously lower in spring (959.9 g/m2) with an obvious accumulation at the 60–80 cm soil depth compared to fall (1124.6 g/m2). Topsoil concentration factors also indicated that TP and AP had shallower distribution in soil profiles. Correlation analysis showed that AP had significant and positive correlation with these soil properties such as soil organic matter, salinity, total nitrogen and Al (p < 0.01), but TP was just significantly correlated with TN and Al (p < 0.05).

Impacts of Thirty‐Seven Years of Stocking on Soil Phosphorus Distribution in Bermudagrass Pastures

Pasture management affects soil properties, but information concerning the effects of long‐term stocking and fertility regimens on soil P in pastures is limited. This study investigated changes in extractable soil P concentrations from Coastal and common bermudagrass [Cynodon dactylon (L) Pers.] pastures stocked for 37 yr at different intensities on an Ultisol. From 1969 through 2004, pastures were continuously stocked during February to September to achieve high, medium, and low herbage mass. Annual fall‐applied P averaged 44 kg ha–1 from 1969 to1984 and 51 kg ha–1 from 1998 to 2004. Extractable soil P concentrations in the 0‐ to 15‐cm depth increased (P ≤ 0.0001) from 5 mg kg–1 (very low) in 1975 to 43 mg kg–1 in 2004 (high), and deeper depths showed 14 to 36% increased P levels. Elimination of P fertilizer for 13 yr, 1985 to 1997, decreased (P ≤ 0.0001) extractable soil P in the 0‐ to 15‐cm depth by 30 and 47% in common and Coastal bermudagrass pastures, respectively. An interaction between year and stocking rate was evident as extractable P levels increased after 20 yr at high stocking rates. After 37 yr, extractable P levels at the 0‐ to 120‐cm soil depth followed the order high &gt; medium ≥ low stocking rate. Despite the effect of stocking rate on soil P, 37 yr of continuous stocking showed no evidence of excessive P accumulation at levels that may pose an environmental threat. Phosphorus recycled through the soil–forage–animal system sustained adequate forage and animal productivity.

Do P Cycling Patterns Differ Between Ice-Free Areas and Glacial Boundaries in the Maritime Antarctic Region?

Antarctic studies have indicated that during summer, ice-free areas experience greater temperatures than those along the glacial boundaries. This allows for the availability of liquid water and thus influences the biogeochemical processes of Antarctic terrestrial ecosystems. In this study we explore whether the patterns of soil phosphorus cycling differ between the glacial boundary and ice-free areas. To do so, we chose two sites on the Fildes Peninsula in Antarctica, one at the boundary of the Collins Glacier and another within an ice-free area close to Lake Uruguay. In each location, we determined soil phosphorus distribution, iron and aluminum fractions, soil mineralogy, alkaline phosphatase activity, and fluorescein diacetate hydrolysis. The results showed that soils of the ice-free area had a greater content of phosphorus sorbed on iron/aluminum oxyhydroxides and occluded forms. An opposite pattern was obtained for the calcium-bound phosphorus pool. Accordingly, soil samples from the ice-free area showed the greatest levels of iron/ aluminum oxyhydroxides and the presence of secondary minerals such as hematite and the intergrade chlorite-vermiculite-montmorillonite. Alkaline phosphatase activity and the fluorescein diacetate hydrolysis were also favored at the ice-free area. The overall results suggest that the less extreme microclimatic conditions and the presence of liquid water in the ice-free area promote the biogeochemical cycling of soil phosphorus. In a context of climate warming this study may contribute to the comprehension of how the expansion of the ice-free areas due to glacial retreat influences biogeochemical cycling of essential nutrients in the Antarctic Peninsula.

The distribution of soil phosphorus for global biogeochemical modeling

Abstract. Phosphorus (P) is a major element required for biological activity in terrestrial ecosystems. Although the total P content in most soils can be large, only a small fraction is available or in an organic form for biological utilization because it is bound either in incompletely weathered mineral particles, adsorbed on mineral surfaces, or, over the time of soil formation, made unavailable by secondary mineral formation (occluded). In order to adequately represent phosphorus availability in global biogeochemistry–climate models, a representation of the amount and form of P in soils globally is required. We develop an approach that builds on existing knowledge of soil P processes and databases of parent material and soil P measurements to provide spatially explicit estimates of different forms of naturally occurring soil P on the global scale. We assembled data on the various forms of phosphorus in soils globally, chronosequence information, and several global spatial databases to develop a map of total soil P and the distribution among mineral bound, labile, organic, occluded, and secondary P forms in soils globally. The amount of P, to 50cm soil depth, in soil labile, organic, occluded, and secondary pools is 3.6 ± 3, 8.6 ± 6, 12.2 ± 8, and 3.2 ± 2 Pg P (Petagrams of P, 1 Pg = 1 × 1015g) respectively. The amount in soil mineral particles to the same depth is estimated at 13.0 ± 8 Pg P for a global soil total of 40.6 ± 18 Pg P. The large uncertainty in our estimates reflects our limited understanding of the processes controlling soil P transformations during pedogenesis and a deficiency in the number of soil P measurements. In spite of the large uncertainty, the estimated global spatial variation and distribution of different soil P forms presented in this study will be useful for global biogeochemistry models that include P as a limiting element in biological production by providing initial estimates of the available soil P for plant uptake and microbial utilization.

Soil Phosphorus Distribution as Affected by Irrigation Methods in Plastic Film House

Water-saving irrigation methods have been increasingly used for vegetable cultivation in greenhouse or plastic film house. However, there is limited information concerning the effect of water-saving irrigation methods on soil phosphorus (P) behavior. In this experiment, drip and subsurface irrigation methods were applied, with furrow irrigation method as control, in Mollic Gleysols. Soil P distribution throughout the depth was significantly affected by irrigation methods. Total, Olsen, organic and inorganic P contents were greater in the topsoil (0–10 and 10–20 cm) than in the subsoil (20–30, 30–40, 40–50 and 50–60 cm). The Olsen P content throughout 0–60 cm layer under drip and subsurface irrigation treatments was lower than that under the furrow irrigation treatment. However, the total, organic and inorganic P contents from 20 to 60 cm under drip irrigation treatment were higher than or close to those under furrow irrigation treatment, but were lower under subsurface irrigation treatment than under furrow irrigation treatment. Under subsurface irrigation treatment, the contents of total, organic and inorganic P at the 0–10 cm layer were 78.0%, 1.3% and 3.7% greater than those at the 10–20 cm layer, respectively. But Olsen P content at the 10–20 cm layer was 5.7% larger than that at the 0–10 cm layer. These suggested that soil P behavior could be manipulated by soil water management to some extent.

Regional Distribution of Soil Phosphorus Across Congregation-Grazing Zones of Forage-Based Pastures with Cow-Calf Operations in Florida

The arrangement of supplemental feed, water, shelter, and their concurrent interactions with topographic features may influence the distribution of animals and their simultaneous use of pasture’s resources. The effects of grazing and/or congregation management that control phosphorus cycling and distribution have not been sufficiently evaluated. The objectives of this study were: 1) to determine whether cattle congregation sites typical on most Florida ranches, repre-sented by water troughs and shaded areas, are more phosphorus-rich and may contribute more soluble phosphorus to surface water run-off and groundwater than other pasture locations; and 2) to assess the regional distribution of Mehlich-1 extractable soil phosphorus (MP) across congregation-grazing zones of forage-based pastures with cow-calf operations in Florida. Soil samples were collected at increasing distance from congregations structures (water troughs and shades) in established (>10 yr), grazed beef cattle pastures located in three Florida regions. Samples were col-lected in the fall and spring of 2005, 2006, and 2007, respectively; following a radial (every 90 degrees) sampling pat-terns away from the center of the congregation structures. Averaged across years, MP and soil phosphorus saturation in the congregation zones were comparable (p ≤ 0.05) with MP values and soil phosphorus saturation in the grazing zones at all three Florida regions. Average MP at all three pasture locations did not exceed the crop requirement threshold of 50 mg P kg–1 and the water quality protection threshold of 150 mg P kg–1, suggesting that congregation zones in beef cattle pastures at all three regions of Florida are not phosphorus-rich.

Long-Term Fertilization Effect on Fraction and Distribution of Soil Phosphorus in a Plastic-Film House in China

Knowledge of phosphorus (P) behavior in long-term fertilized soils is essential for better fertilization practices and protection of environmental quality. Therefore, we evaluated the various forms of P contents, fraction, and distribution of soil inorganic P in a greenhouse under continuous fertilization since 1988. Continuous fertilization increased total and available P contents at the 0- to 20-cm soil layer. Applied organic manure and chemical fertilizer increased the contents of total, available, organic, and inorganic P (Pi) significantly. In the soil fertilized with organic manure, the greatest fraction of the Pi was occluded P (O-P), whereas in the soil not fertilized with organic manure, the greatest fraction of the Pi was calcium-bound P (Ca-P). All fractions of the Pi in both soils treated with organic manure and inorganic manure decreased gradually with soil depth. Thus, the long-term fertilization of organic fertilizer increases the accumulation of various soil P forms and causes deeper Pi translocation.

Spatial distribution of soil phosphorus and herbage mass in beef cattle pastures: effects of slope aspect and slope position

Characterizing and assessing spatial distribution of soil phosphorus and herbage mass in relation to landscape properties, land use, or landscape positions is important for understanding how pasture sustainability can be managed and improved properly. Our reason for conducting this study was to determine the effects of different slope aspects and slope positions on spatial distribution of soil phosphorus and herbage mass in subtropical pastures. Soil and forage samples were collected from contiguous south-, north-, east-, and west-facing slopes across different landscape positions (top slope, middle slope, and bottom slope) in 100 ha of bahiagrass (Paspalum notatum)-based pastures from 2003 to 2006 in subtropical region of southeastern USA. Averaged across years, soils on the north-facing slope contained the greatest amount of soil phosphorus (12.4 ± 2.7 mg kg−1) when compared with other slope aspects. Slope aspect may be acting as an important topographic factor influencing local site microclimate mainly because it determines the amount of solar radiation received. The greatest herbage mass (averaged across year) of 2,967 ± 980 kg ha−1 and the highest phosphorus accumulation of 7.7 ± 3.0 kg ha−1 for bahiagrass were from the top slope position. There was a significant (P ≤ 0.05) decrease in the average herbage mass and phosphorus accumulation with decreasing slope (top to middle slope). Between the top slope and the bottom slope, herbage mass declined from 2,967 ± 980 to 1,805 ± 370 kg ha−1 while phosphorus accumulation was reduced by approximately 40% (7.7–4.6 kg ha−1). Results of our study may increase awareness on how the arrangement of food, water, and shelter and their interactions with topographic and landscape features can significantly influence the movement of animals and utilization of different pastures’ resources. While our study supports our hypothesis that slope aspect and slope position could be of relative importance in controlling spatial distribution of soil phosphorus and herbage mass, broad knowledge of cattle movement in pasture situations is as critical to understanding their impact on agro-ecosystems.

Phosphorus Fertilization in Rice (&lt;i&gt;Oryza sativa&lt;/i&gt; L) Cultivation Changes Soil P-Fractions

A study was conducted at the BRRI research farm during 2001 to determine the distribution of soil phosphorus (P) fractions in P-deficient rice soil that received varied amount of P as triple super phosphate (TSP) and di-ammonium phosphate (DAP). Solution P ranged from 0.06 to 0.08 mg L-1 which was significantly greater in long duration variety (LDV) compared to short duration variety (SDV) at Pcontrol conditions. The increase in NaHCO3-Pi pool was 4.5-35.2% greater with LDV compared to SDV at 30-45 kg P ha-1. There was 7-10% greater NaOH-Po after growing LDV compared to SDV at larger P doses as TSP. The buildup of NaOH-Po pool was greater by 18% after growth of SDV compared to LDV when P was added as DAP. The NaOH-Pi fraction increased by about 21-212% with P application compared to P control irrespective of P sources. The larger HCl-Pi fraction buildup (21-152%) took place because of P application either as TSP or DAP, especially with the LDV. The increase in residual-P fraction was 10-158% because of P-fertilization and rice genotypes compared to control. Under Pfertilized conditions, NaHCO3-Pi and NaOH-Po appeared to have acted as sinks of added P-fertilizer. Cultivation of rice genotypes at 30-40 kg P ha-1 under lowland situations further contributes to P buildup in soil which could be utilized in the succeeding crops for profitable farming.

Soil phosphorus distribution in sequentially extracted fractions in tropical coffee-agroecosystems in the Atlantic Forest biome, Southeastern Brazil

Phosphorus (P) deficiency is one of the most important constraints to food production, particularly in tropical Oxisols. This study aimed to characterize the inorganic and organic P (Pi and Po) fractions in the soil in three smallholding coffee cultivation fields managed under either agroforestry (AGF) or full sun (FSC) agroecosystems. The work was carried out in areas situated at the municipalities of Divino and Araponga in the Zona da Mata in the state of Minas Gerais, southeastern Brazil. Soil P forms including H2O–Pi; NaHCO3–Pi,Po; NaOH–Pi,Po; diluted HCl–Pi; concentrate HCl–Pi,Po and Residual-P were sequentially extracted in samples from 0 to 5 and 5 to 10-cm soil layers. Together, H2O–Pi and NaHCO3–Pi accounted on average for only 4% of soil total P in the cultivated soils. HClconc.-Pi ranged from 142.8 to 372.4 mg kg−1 being the predominant Pi fraction. AGF systems promoted an increment of 8% in the NaHCO3–Po fraction in relation to the FSC systems in the upper soil layer. The AGF systems increased HClconc.-Po pool in relation to the FSC systems in Divino and Araponga(I) soils, indicating that agroforestry is an important management strategy to increase bioavailable P and for the maintenance of organic P pool. The distribution of inorganic and organic P pools varied among the different study sites, showing that P cycling depends on the inherent characteristic of each agroecosystem. The availability of P to plants in coffee-agroforestry fields is directly associated with the cycling of the organic P pool.

Soil Phosphorus Distribution as Affected by Manure Compost Phosphorus Concentration and Incorporation

Phosphorus (P) from manure can become an environmental pollutant if applied to soil at rates in excess of plant uptake. This research examined the effects of composted beef cattle manures from two feeding regimens on soil P storage and forms. Composted manures were applied in the spring before planting (preplant) with incorporation, in spring after planting (postplant) without incorporation, or in winter without incorporation. Soils were sampled following 1 and 2 years of treatment at depths to 15.0 cm. All P fractions from both composted manures increased over pre-amended levels. High-P composted manure increased total P (TP) and inorganic P (IP) more than low-P composted manure. Total P and IP were greater in soils receiving low-P composted manure postplant than in those receiving manure preplant. Accumulation of TP and IP in uppermost depths was greater in the second year of composted manure application than in the first year. Appropriately managing composted manure requires integrating P concentration, time of application, and incorporation.

Distributions of soil phosphorus in China’s densely populated village landscapes

Purpose Village landscapes, which integrate small-scale agriculture with housing, forestry and a host of other land use practices, cover more than 2×10 6 km 2 across China. Village lands tend to be managed at very fine spatial scales (≤30 m), with managers altering soil fertility and even terrain by terracing, irrigation, fertilizing, and other land use practices. Under these conditions, accumulation of excess phosphorous in soils has become important contributor to eutrophication of surface waters across China’s densely populated village landscapes. The aim of this study was to investigate relationships between fine-scale patterns of agricultural management and soil total phosphorus (STP) within China’s village landscapes. Materials and methods First, China’s village landscapes weredividedinto five environmentallydistinctregions across China. Within each region, a single 100 km 2 research site was then selected, and 12 500×500 m square landscape sample cells were selected for fine-scale mapping. Soils were sampled within fine-scale landscape features using a regionally weighted landscape sampling design. Results and discussion STP stock across the 0.9×10 6 km 2 area of our five village regions was approximately 0.14 Pg (1 Pg=10 15 g), with STP densities ranging from 0.08 kg m −2 in Tropical Hilly Region to 0.22 kg m −2 in North China Plain and Yangtze Plain, with village landscape STP density varying significantly with precipitation and temperature. Outside the Tropical Hilly Region, STP densities also varied significantly with land form, use, and cover. As expected, the highest STP densities were found in agricultural lands and in areas near buildings, while the lowest were in nonproductive lands and forestry lands. As a combined result of these high STP densities and the predominance of agricultural land use, most village STP stock was found in agricultural lands. A

Organic and inorganic phosphorus in Mollisol soil under different tillage practices

The distribution of soil phosphorus (P) between different organic and inorganic forms depends on, among other factors, the tillage systems. The evaluation of soil P fractions is essential to determine if they are related to available P. The objective was to characterize the P forms from a soil under no tillage (NT) and conventional tillage (CT). Soil samples were taken at 0–5, 5–10 and 10–20 cm depth from a fine, mixed, thermic Petrocalcic Paleoudoll, after 8 years under NT and CT. Inorganic and organic P was measured in the anion exchange membrane (AEM), NaHCO 3, NaOH, NaOH after sonication, HCl and residual fractions extracted sequentially. Microbial P was determined by fumigating with chloroform after P extraction with AEM. The tillage systems did not affect the total P content but the distribution of P among fractions changed between NT and CT. No tillage system had significantly higher microbial P at all soil depths and ranged from 34 mg P kg −1 at 0–5 cm to 10 mg P kg −1 at 10–20 cm. In the upper 10 cm of soil, NT tended to have higher AEM-Pi and NaHCO 3-Pi comparing to CT system. The increase in AEM-Pi was closely related to organic carbon increases and pH decreases. The was a consistently higher concentration of NaOH-Po but the increase was significant al 5–10 and 10–20 cm, and represented on average about 35% of total P. The residual P which was considered mostly organic was also an important pool in both NT and CT, and accounted for about 30% of total P. Therefore, P availability is mainly controlled by organic P which makes up a larger proportion of total P.

Forms and profile distribution of soil phosphorus in four wetlands across gradients of sand desertification in Northeast China

Little is known about the relationship between soil phosphorus (P) forms of semiarid wetlands and surrounding upland land-use patterns. Soil P in different depths of four wetlands was fractionated using a modified Hedley fraction method. The wetland soil cores were sampled along a gradient of sand desertification in the west of Songnen Plain (Northeast China), and sectioned with high-resolution (2-cm intervals). The soil total P (P t) content and P forms varied significantly within and among the profiles with strongly alkaline (pH 7.9 to 10.5) in sand and no sand desertification wetlands. The P t mean content ranged from 90.8 to 231.6 mg/kg in the sand desertification wetlands, and 421.3 mg/kg in the no sand desertification wetland. Dilute HCl extractable inorganic P (P i) is the predominant form in all profiles, both as absolute values and as a percentage of total extracted P i (mean: 56–77%), and concentrated HCl extractable organic P (P o) is the predominant form of total extracted P o (mean: 45–68%). Moreover, Dil.HCl–P i and Conc.HCl–P i were strongly positive correlated with the content of Al, Ca, Fe, clay and silt percentages, but negative correlated with sand percentages. All forms of organic P (NaHCO 3–P o, NaOH–P o, and Conc.HCl–P o) were strongly positive correlated with the content of total organic carbon (C org). In addition, for comparison of soil heterogeneity affected by sand desertification, uplands surface soil samples were collected from grassland, cultivated land, and sand lands surrounding the four representative wetlands. The results indicated that P forms of the surface soils were significantly different among studied upland land-use patterns. Consequently, there were general differences in soil P forms between sand and no sand desertification wetland profiles. The Residual–P heterogeneity in the wetland profiles can partly be attributed to the influences of different intensity of sand desertification. And Residual–P could be as an index of the intensity of desertification.

Phosphorus acquisition and wheat growth are influenced by shoot phosphorus status and soil phosphorus distribution in a split‐root system

AbstractRoot proliferation and greater uptake per unit of root in the nutrient‐rich zones are often considered to be compensatory responses. This study aimed to examine the influence of plant phosphorus (P) status and P distribution in the root zone on root P acquisition and root and shoot growth of wheat (Triticum aestivum L.) in a split‐root soil culture. One compartment (A) was supplied with either 4 or 14 mg P (kg soil)–1, whereas the adjoining compartment (B) had 4 mg P kg–1 with a vertical high‐P strip (44 mg kg–1) at 90–110 mm from the plant. Three weeks after growing in the split‐root system, plants with 4 mg P kg–1 (low‐P plants) started to show stimulatory root growth in the high‐P strip. Two weeks later, root dry weight and length density in the high‐P strip were significantly greater for the low‐P plants than for the plants with 14 mg P (kg soil)–1. However, after 8 weeks of growth in the split‐root system, the two P treatments of compartment A had similar root growth in the high‐P strip of compartment B. The study also showed that shoot P concentrations in the low‐P plants were 0.6–0.8 mg g–1 compared with 1.7–1.9 mg g–1 in the 14 mg P kg–1 plants after 3 and 5 weeks of growth, but were similar (1.1–1.4 mg g–1) between the two plants by week 8. The low‐P plants had lower root P concentration in both compartments than those with 14 mg P kg–1 throughout the three harvests. The findings may indicate that root proliferation and P acquisition under heterogeneous conditions are influenced by shoot P status (internal) and soil P distribution (external). There were no differences in the total root and shoot dry weight between the two P treatments at weeks 3 and 5 because enhanced root growth and P uptake in the high‐P strip by the low‐P plants were compensated by reduced root growth elsewhere. In contrast, total plant growth and total root and shoot P contents were greater in the 14 mg P kg–1 soil than in the low‐P soil at week 8. The two P treatments did not affect the ratio of root to shoot dry weight with time. The results suggest that root proliferation and greater P uptake in the P‐enriched zone may meet the demand for P by P‐deficient plants only for a limited period of time.

Soil phosphorus cycling in an Antarctic polar desert

Soil phosphorus distribution and cycling in the McMurdo Dry Valleys is poorly understood despite its importance for contemporary Antarctic ecosystem processes. We present data from sequential chemical extractions of phosphorus pools from dry valley soils and sediments on tills across a gradient of surface exposure ages, and across potential weathering gradients in stream channels. The geologically old, but poorly weathered, soils of the dry valleys have large phosphorus pools relative to in situ biological requirements. These pools are dominated by unweathered P fractions, comprising between 60 and 90% of total soil phosphorus among sites occurring on tills ranging in surface exposure ages of approximately 10 3–10 6 yrs. Variation in total phosphorus concentration and availability are related to differences in the initial P content of these tills; Ross Sea tills contain basalts and kenyte which contribute to higher concentrations of phosphorus relative to soils developing on tills deposited by advances of the Taylor Glacier. At local scales, physicochemical gradients contribute to variation in weathering rates, altering the distribution of phosphorus among chemical fractions, which differ in their potential mobility and availability to microorganisms. For example, hyporheic stream sediments exhibit evidence of phosphorus weathering from primary minerals and loss relative to upland soils adjacent to stream channels. Dry valley landscapes (glaciers, lakes streams, soils) are hydrologically connected, providing a mechanism for phosphorus weathering and mobilization in soils and sediments to contribute to the nutrient budgets of adjacent aquatic ecosystems. We suggest that landscape history (till composition) and contemporary subsurface and stream hydrology are the primary controls over phosphorus cycling in the McMurdo Dry Valleys.

Comparison of Organic and Inorganic Phosphorus Fractions in an Established Buffer and Adjacent Production Field

Since the U.S. Department of Agriculture's Conservation Reserve Program was established in 1985, thousands of acres of cropland have been converted to conservation buffers. The distributions of soil phosphorus (P) in various organic and inorganic fractions in a buffer and an adjacent crop production field were compared. Most of the extractable inorganic P (32 to 39%) in both the crop field and the buffer was present in the calcium (Ca)‐P fraction. Levels of the most labile P fractions were higher in the cropped area; however, more P was in the iron (Fe)‐P fraction in the buffer (23 vs. 18%). There were few differences among organic P fractions between the buffer and crop field. Soil sampling depth had a significant effect on the distribution of P. Differences between the cropped area and the buffer were less significant as depth increased. These results suggest that care should be taken in choosing sampling depths when relating P fraction distribution to potential P loss.

Implications of soil organic carbon and the biogeochemistry of iron and aluminum on soil phosphorus distribution in flooded forests of the lower Orinoco River, Venezuela

Relationships among soil phosphorus distribution, soil organic carbon and biogeochemistry of iron and aluminum were studied along a flooded forest gradient of the Mapire river, Venezuela. Soil samples were collected during the dry season in three zones subjected to different flooding intensity: MAX inundated 8 months per year, MED inundated 5 months per year, and MIN inundated 2 months per year. Total labile phosphorus (resin + bicarbonate extractable fractions) was significantly higher in MIN than in MAX. The longer non-flooding period in MIN probably allowed a higher accumulation of microbial biomass in soils of this zone and consequently a greater release of the bicarbonate organic fraction. The moderately labile phosphorus fraction associated with the chemisorbed phosphorus on amorphous and some crystalline aluminum and iron was significantly lower in MAX than in MIN following the same tendency observed for crystalline iron oxides. This result allowed us to hypothesize that the combined effect of a long flood period and a high soil organic carbon content in the MAX, could be appropriate conditions for microbial reduction of stable forms of iron. The ratio of soil organic carbon to total organic phosphorus decreased from MAX to MIN, indicating higher mineralization of organic phosphorus in MIN. Our results suggests two distinct flood-dependent mechanisms operating for phosphorus release along the gradient. In MAX mineralization process appears to be limited, while microbial mineral dissolution appears to be an important source of phosphorus. In MIN supply of phosphorus is associated with the stability of soil organic matter.